Do you have any good techniques for using Tufa ? I have
a few big pieces laying around in my studio and would love to
Native American “sandcast” pieces, usually featuring najas (the
main horseshoe shape of the squash blossom necklace), ketos
(bowguards), buckles and sandcast bracelets began their lives as
tufa carvings. These designs were heavily influenced by the
Spanish who used them as forestall and headstall decorations on
their horses. A carving is made in tufa stone and cast. This
becomes the master model for casting in sand or cement.
Because of the nature of casting in tufa, which has to rely on
the force of gravity alone to get the molten metal to all areas
of the design, you have to plan your design with this in mind.
Most of these pieces are visually and physically massive. You
must plan for sizeable bridges between each part of the design.
This is why you’ll often see the design in either half-round or
triangular shapes for the pattern. Think of designing with
either half-round or triangular wire.
You need two blocks of tufa for each carving. You will carve a
bas-relief in the negative on one half. The other half is the
flat back. Both blocks need to have the sprue hole cut into them
however, half of the sprue on each block.
After both blocks have been trued, lay out your pattern you
intend to carve on one block. Leave about 1/2" uncarved stone for
very small castings, proportionately larger for larger carvings.
Often, I just use a pencil to draw directly onto the stone. My
favorite tools for carving the tufa are my wax tool (which
dentists call a carver), a scooped spatula wax tool and a small
paring knife. After the carving is done, check your bridges, add
sprue and air vents.
Next stabilize the carving with aqueous sodium silicate which
has been thinned out with water (50/50 ratio) by painting it on
all sides and allow it to dry thoroughly. This stabilization
process can also be used to preserve your cuttlefish carvings.
This makes it hard so you can use it for several castings, but
the first casting should always be saved for your master. This is
usually cast in bronze, which is then used to make sand castings
after it’s been cleaned up.
Soot up the casting sides of both blocks generously. Use a brush
to remove any excess soot. The soot allows you to remove the
casting without it sticking to the stone and pulling out your
carved design, but any loose soot can be carried into the casting
and ruin it. Bind the two halves together with wire and cast
Until you get the hang of how large your bridges need to be, the
depth of the carving and so-on, start with small designs. You’ll
get the idea very quickly and will then be able to progress to
I hope this helped to answer your questions and you’ll start
using those pieces of tufa laying around. KP in Wyoming